Our invention relates to apparatus employing disklike record media for the recording and/or reproduction of data, and more specifically to apparatus for data transfer with flexible magnetic disks, now commonly referred to as floppy disks, although we do not wish our invention to be unnecessarily limited to this particular type of record medium. Still more specifically, our invention concerns a device known as a floppy disk drive (FDD) for data transfer to and from interchangeable floppy disks, featuring provisions for avoiding waste of power.
Floppy disks have found widespread acceptance in information processing and allied industries, as well as in offices and homes, as compact data storage media. Being thin and limply flexible, the disks are usually encased in more rigid, apertured envelopes to make up disk cartridges or cassettes that are self supporting. There have also been suggested and used a variety of FDDs for data transfer to and/or from such disk cartridges or cassettes. U.S. Pat. No. 4,089,029, issued May 9, 1978 to Castrodale et al. and assigned to International Business Machines Corp., represents a familiar example of floppy disk and FDD combination, and a different floppy disk and FDD combination has more recently been proposed by Sony Corp., as disclosed in Japanese Laid Open Patent Application No. 57-36473, laid open to public inspection on Feb. 27, 1982, and in corresponding U.S. Pat. No. 4,445,155 issued Apr. 24, 1984.
Usually, FDDs are not self contained; they are slave units under the control of master equipment typically comprising a central processor unit (CPU) and an associated FDD controller. Each FDD intended for use with such master equipment has no power switch of its own. In a data processing system comprising a CPU, an FDD controller, and one or more FDDs, for example, only one power switch serves the complete system.
A problem has existed with respect to the power consumption of such a data processing system. Power has conventionally been fed to and consumed by the various components of the FDD or FDDs upon closure of the system power switch. However, not all the FDD components need by powered at all times during the operation of the data processing system. Take, for example, the photoelectric sensors incorporated in each FDD. Although the outputs from the sensors are utilized for the purposes for which they are intended only for limited lengths of time during the operation of the data processing system, the light sources of the sensors have been held energized throughout the complete period of system operation. This of course has incurred a substantial waste of energy.